This invention concerns the provision of wear resistant surfaces on ground working implements. It has particular but not exclusive application to wear-prone ground-engaging components used on agricultural cultivator components, such as tillage points plough shares, plough discs and the like, and on mining and earth-moving equipment.
This specification uses the term xe2x80x9ctillage pointxe2x80x9d in its meaning as a general term which includes the type of agricultural tips or points used for scarifiers, sweeps, ground busters, seeder combines, direct drills and the like.
Farmers often routinely modify presently available tillage points by, for example, laying on hard facing materials from welding rods, or by welding onto the points additional metal such as stainless steel bolts. Longer tip life may be achieved but usually at the cost of significantly higher fuel consumption from the machinery pulling the modified points.
Great effort has been expended by many people in recent decades to develop harder and tougher steels and other materials for the manufacture of ground working implements such as the replaceable tips intended to engage and work the ground when mounted on agricultural and earth moving machines. It is known for such implements to have been constructed entirely of such newly developed alloys and systems have been developed for bonding inserts, such as tungsten carbide strips, or coatings of such harder materials onto the wearing edges. However such sophisticated alloys are relatively expensive, and hard inserts such as tungsten carbide have a tendency to fracture when cultivating ground containing rocks.
In the case of the common arrowhead shaped tillage points used on agricultural equipment, prior art developments have concentrated on protecting the upper surface of the leading edge of the point. An example of this type of development can be seen in patent specification AU-A-74010/91.
It is not only harder materials that have been proposed for this purpose. Patent specification WO 97/14291 describes how a point for an agricultural scarifier may be constructed with a polyurethane material applied to its outer surface in order to reduce wear of the scarifier point. The point has a core plate having a series of protrusions, indentations and holes formed in it and these help prevent separation of the protective polyurethane coating from the core plate during use.
It has now been observed that points made in accordance with the above patent specification WO 97/14291 can have a tendency for the polyurethane to delaminate from the steel substrate, particularly after the steel has partially worn away and particularly on the upper surface of the point. The present invention is directed to an alternative configuration whereby the likelihood of such delamination is greatly reduced.
Accordingly, in one aspect the invention provides a ground working implement having a cutting edge, said implement being formed from a rigid body of substrate material and a wear resistant coating applied to a face of the body up to the cutting edge, the coating adjacent the cutting edge having a cut, a trench or a line of weakness formed therein substantially parallel to the edge. Preferably the coating adjacent the cutting edge has a series of parallel cuts, trenches or lines of weakness formed therein substantially parallel to the edge. Preferably the coating is softer and more flexible than the substrate material and is preferably a polyurethane based plastics material. The implement may have a mounting portion by which the implement is adapted to be attached to an agricultural ground working implement and have a generally triangular shaped working portion comprising a nose portion and a pair of wings swept back therefrom, with the leading edge of the nose and wings forming said cutting edge.
In another aspect the invention provides a tillage point constructed as a metal body with wear resistant plastics material affixed thereto, said tillage point having a mounting portion by which it is adapted to be attached to an agricultural ground working implement and having a generally triangular shaped working portion comprising a nose portion and a pair of wings swept back therefrom, with the leading edge of the nose and wings forming a cutting edge and the metal at the rear of the nose portion stepped in order to protect the leading edge of the plastics material immediately behind the nose. Preferably the metal body is formed from sheet metal and, when aligned as for use, has the nose portion upwardly displaced to create said step. Preferably the upper surface of the nose does not carry a wear resistant covering of plastics material. Preferably a pad of wear resistant material fills the underside of the nose portion.
The wear resistant plastics material may be a polyurethane material bonded to the metal body in an injection moulding operation wherein the metal body is placed within the injection moulding die.